Enzymes

Question 1

Enzymes

Answer 1

BIological catalysts that increase the rate of a biochemical reaction while remaining unchanged at the end of the reaction

Question 2

Contact residue

Answer 2

AA residues that form the shape of the active site that is complementary to the substrate

Question 3

Catalytic residues

Answer 3

AA residues that catalyse the biochemical reaction by increasing the reactivity of the substrate

Question 4

Lock and key hypothesis

Answer 4

• Substrate completely complementary in shape to active site
• Shape of active site unchanged
• Enzymes can only bind to substrate if they are in the right orientation (effective collision)

Question 4

Induced fit hypothesis

Answer 4

• The initial shape of the active site is not completely complementary to the substrate
• When the substrate binds to the active site, a slight conformational change occurs
• Hence substrate fits more snugly

Question 5

How enzymes lower E_a

Answer 5

1. The r-groups of catalytic residues are very close to portions of the substrate and can alter the distribution of electrons within the bonds of the substrate
2. Different substrate moelcules are forced together into the right orientation, facilitating bond formation
3. Certain bonds in the substrate molecules may be under physical stress

Question 6

Q₁₀ temperature coefficient

Answer 6

rate at (T+10) / rate at T°C = 2

Question 7

Effect of increase vs decreasing pH

Answer 7

Identical except for charges

Question 8

V_max

Answer 8

The maximum rate of an enzymatic reaction at give enzyme concentration, temperature and pH. (in the presence of excess substrate)

Question 9

Michaelis-Menten Constant, K_m

Answer 9

The substrate concentration that enables an ezymatic reaction to proceed at half its maximum rate of 1/2 V_max.

Its constant for a particular enzyme

Question 10

Enzyme affinity

Answer 10

Calculated by the inverse of K_m

Question 11

Competitive inhibitors

Answer 11

• Inhibitor has a close structural resemblance to substrate and thus is complementary to enzyme active site
• Lowers enzyme affinity
• If substrate concentration is sufficiently high, it can outcompete the inhibitor

Question 12

Non-competitive inhibitor

Answer 12

• Inhibitor binds to the enzyme at a site other than the active site
• Inhibitor causes conformational change in enzyme, active site no longer complementary
• K_m and enzyme affinity unaffected

Question 13

Allosteric enzyme

Answer 13

• Can alternate between high affinity active forms and low affinity inactive forms
• Due to cooperativity phenomenon, allosteric enzymes have a sigmodial shaped graph

Question 14

Cooperativity

Answer 14

When one substrate binds to the active site of the enzyme, the enzyme’s conformation turns to its active form, facilitating other substrate binding at other active sites